This is the usual viral electric build. Feel free to switch it to blast electric or gas electric. They're all pretty fun to use.

The heat damage gimmick on this weapon is as follows: "Increasing combo multiplier grants 4% heat damage for 15s. Stacks up to 30x". Thankfully, the heat damage that builds from the combo counter does not mix with electric, so you can still use Melee Influence.

The issue is that once you hit 12x combo, the heat damage gimmick does not increase any further, so you actually want to waste the combo multiplier you built up so that you can increase the heat damage stack. For this reason, I have [Relentless Combination] to help build up the combo counter fast and increase that heat damage stack up to 30x.

To keep the heat damage, you also have to continuously build your combo counter up, so you have to keep using your heavy attack outside of Tennokai.
Frankly, as mentioned in the comments, it might be better to replace the Tennokai mod in favor of [Dispatch Overdrive]. Otherwise, if you still want a Tennokai mod, I recommend [Condition's Perfection] since it'll add more status.

As per the suggestion in the comments, you can add [Galvanized Reflex] in place of [Relentless Combination] if you want. It will generate a 5x combo automatically, so you can keep doing heavy attacks to build up and refresh the heat damage stacks. The only issue is that it will only provide 2 stacks instead of the full 5 stacks. It's definitely a good switch since it offers consistency in letting you refresh your stacks. I find [Relentless Combination] to help more in reaching the 30x stack faster for me and I don't really mind building up my combo counter from 0 since it gains so quickly. Certainly try [Galvanized Reflex] out for your benefit.